Thermal intermediate apparatus, systems, and methods

ABSTRACT

Apparatus and system, as well as fabrication methods therefor, may include a thermal intermediate structure comprised of a plurality of carbon nanotubes some of which have organic moieties attached thereto to tether the nanotubes to at least one of a die and a heat sink. The organic moieties include thiol linkers and amide linkers.

TECHNICAL FIELD

The subject matter relates generally to apparatus, systems, and methodsused to assist in transferring heat from one element or body, such as acircuit, to another, such as a heat sink.

BACKGROUND INFORMATION

Electronic components, such as integrated circuits, may be assembledinto component packages by physically and electrically coupling them toa substrate. During operation, the package may generate heat which canbe dissipated to help maintain the circuitry at a desired temperature.Heat sinks, including heat spreaders, may be coupled to the packageusing a suitable thermal interface to assist in transferring heat fromthe package to the heat sink.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section view of an apparatus according to variousembodiments;

FIG. 2 is a schematic illustration of the functionalization process usedto apply linking organic moieties to the carbon nanotubes;

FIGS. 3-5 are illustrations of various thermal intermediate structureembodiments;

FIGS. 6 and 7 illustrate a process and a method embodiment; and

FIG. 8 is a depiction of a computing system according to an embodiment.

DETAILED DESCRIPTION

In the following detailed description of various embodiments, referenceis made to the accompanying drawings that form a part hereof, and inwhich are shown by way of illustration, and not of limitation, specificembodiments in which the subject matter may be practiced. In thedrawings, like numerals describe substantially similar componentsthroughout the several views. The embodiments illustrated are describedin sufficient detail to enable those skilled in the art to practice theteachings disclosed herein. Other embodiments may be utilized andderived therefrom, such that compositional, structural, and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure.

Examples and embodiments merely typify possible variations. Individualcomponents and functions are optional unless explicitly required, andthe sequence of operations may vary. Portions and features of someembodiments may be included in or substituted for those of others. Thefollowing detailed description is, therefore, not to be taken in alimiting sense.

FIG. 1 is a cross section view of an apparatus 10 according to anembodiment. Apparatus 10 includes a substrate 12, an electronic circuitdie 14 and a thermal management aid such as a heat sink or an integralheat spreader 16 which is mounted adjacent the die 14 and separated fromit by a gap 17, which has a height h.

In one embodiment, the substrate of die 14 is silicon and has front sideand backside surfaces. The die 14 also has at least one integratedcircuit 20 and solder bump contacts 22 on at least its front sidesurface. The contacts 22 connect with contact pads (not shown) on theupper surface of package substrate 12. In an embodiment, the contacts 22are manufactured according to a commonly used controlled collapse chipconnect (C4) process.

In use, electric signals and power are provided to the integratedcircuit 20 through contacts 20, for example. Operation of the integratedcircuit 20 causes heating of die 14. Heat is transferred from componentsof the integrated circuit 20 through to the body of die 14. In order tomove heat away from die 14, it is conducted to the heat spreader 16through a thermal intermediate structure 24 interposed in the gap 17between them to provide a low resistance thermal path for heat generatedin die 14 to heat spreader 16.

In FIG. 1, the heat spreader 16 includes a top plate 18 and supportingside walls 19. In an embodiment the side walls 19 completely surroundthe die 14. In an embodiment, the heat spreader 16 is coupled to afurther heat sink (not shown) which may or may not be actively cooled.

In an embodiment, the thermal interface structure 24 comprises aplurality 25 of either densely packed multi-walled or single walledcarbon nanotubes 25 or a combination of both single and double wallednanotubes. Carbon nanotubes 25 have a coefficient of thermalconductivity along their longitudinal axis which is relatively highrelative to their conductivity along a path oriented orthogonal to thelongitudinal axis. The thermal conductivity of carbon nanotubes alongtheir longitudinal axes is substantially higher than that of othermaterials used for thermal intermediates. The thermal conductivity ofmulti-walled nanotubes is about 3000 to 4000 W/m-K. The conductivity isabout 6000 W/m-K for single walled nanotubes.

In an embodiment, either the heat spreader 16 or a lower surface of topplate 18 thereof, is formed of, or coated with, gold, a gold alloy orsilver or a silver alloy coating 26 prior to growing the plurality ofcarbon nanotubes 25. In an embodiment, one or both of layers 26 and 30is a layer comprising crystalline gold, Au (111).

In an embodiment, nanotubes 25 may be grown by known methods such as arcdischarge, laser ablation or catalytic chemical ablation. Thoseprocesses produce extended strands of carbon nanotubes, in both singlewalled and double walled states, arranged in randomly tangled nanotuberopes.

In one embodiment, the nanotubes are organized 25 or manipulated toproduce well-ordered arrays for use in thermal intermediate structures34. In one embodiment long ropes of carbon nanotubes can cut into shortlengths of open-ended nanotubes by oxidation in concentrated sulfuricand nitric acids and functionalized to facilitate bonding to a the endsto a surface. Such shortened nanotubes 25 are believed to be open-endedand carboxyl terminated after the above oxidation treatment.

In an embodiment, the carboxyl terminated carbon nanotubes are to betethered to a gold surface by Au—S chemical bonding. Certain linkingorganic chemical moieties having thiol and amide linkers facilitate theforming of a tether or a chemical bond between an end of the nanotubesand the gold surface. The tethering process is carried out, in anembodiment, after the carboxyl terminated short carbon nanotubes arethiol derivatized by reacting with (CH₂)₂—SH while in a suspension suchas an ethanol suspension and may also be aided by the presence of acondensation agent such as dicyclohexylcarbodiimide.

In FIGS. 2A and 2B a schematic view of the treatment of a nanotube ropeis shown. In a first process, in FIG. 2A, the nanotube ropes areoxidized in a solution of nitric and sulfuric acid. A shortened nanotube25 with carboxyl groups 29 attached to at least the ends thereof isshown following the first process. In a second process, shown in FIG.2B, the shortened nanotubes 25 with carboxyl groups is reacted withH₂N—R—SH. The resultant product shown in FIG. 2B has short nanotubestipped with linking organic moieties including amide and thiol linkers.As part of the process linking organic moieties tether one end of someof the carbon nanotubes 25 to a gold surface 26, 30.

After tethering the ends of the nanotubes 25 to the gold surface, theresultant product, in one embodiment, is a self-assembled monolayer ofthiol functionalized nanotubes. The thiol-functionalized nanotubes areimmobilized on the gold layer by Au—S chemical bonding with many of thenanotubes perpendicularly standing on the surface of the gold layer. Inan embodiment, an amide linker is also present, to facilitate thelinking of the nanotubes 25 to the thiol which links to the goldsurface. The short carbon nanotubes which have linking organic moietiesattached to them are thus chemically bonded to the gold surface. In anembodiment, the ends of the nanotubes are tethered to the surface. Theyare tethered at their ends rather than along their longitudinal axessince the thiol and amide bonds form primarily at the ends of thenanotubes 25.

Substantial alignment of the longitudinal axes of many nanotubes of thearray of carbon nanotubes 25 perpendicular to the surface to which theyare tethered occurs so that they are oriented substantiallyperpendicular to the surface of die 14 to provide a direct thermal pathwith low thermal resistance between die 14 and heat spreader 16.

In one embodiment, the lengths of the nanotubes thus formed may be inthe range of at least about 10 nanometers. In another embodiment, thenanotubes can be in the range of 500 to 10,000 nm long. And mostcommonly 500 to 5000 nm long. In one embodiment, the diameters of thesingle walled nanotubes can be expected to be in the range of about 0.8to 4 nm and multi-walled nanotubes in the range of 10 to 100 nm. In oneembodiment, the nanotubes can also be expected to form into aggregatesor bundles where those nanotubes initially bonding to the gold surfacethen serve as nucleation sites for further bonding to unattached tubesin the liquid suspension of nanotubes.

In some embodiments shown in FIG. 3, a gold coating 26 is applied to thesurface of die 14. A set of nanotubes 25 is attached by a thiol basedtether to die 14. In an embodiment the other ends of the attachednanotubes 25 are brought into contact with the surface of top plate 18of heat spreader 16 and form a thermal coupling by the mechanicalcontact of the ends of the nanotubes and the surface. The chemical bondto the die is facilitated by organic moieties having amide linkers toform a bond to the nanotubes and having thiol linkers to facilitatelinking nanotube ends to the surface of gold layer 26. In an embodiment,the gold layer 26 is crystalline gold with lattice orientation (1,1,1)i.e. Au (111). In an embodiment, the resulting nanotube thermalintermediate structure 24 has a height between about 1 and 25 microns.

In some embodiments, shown in FIG. 4, a plurality of nanotubes 25 isshown with both ends of the nanotubes 26 treated with linking organicmoieties to form thiol-links and amide links to the gold 26, 30 and thenanotubes 25 respectively. In an embodiment, as shown in FIG. 4, theheight of the thermal intermediate structure 24 is about one to 25microns. The thermal intermediate structure of the embodiments shown inFIG. 4 would be expected to provide good thermal interfaces between thenanotubes and the surfaces to which they are tethered than the oneillustrated in FIG. 3. Tethering of the nanotubes to both the heatspreader and the die would be expected to reduce the thermal resistanceof the overall heat flow path.

In some embodiments, shown in FIG. 5, the thermal intermediate portion24A is formed by depositing one layer of nanotubes on the surface of die14 and another portion 24B on the surface of heat spreader 16. Thetethering of the nanotubes to the surfaces is again through the use oflinking organic moieties with amide linkers and thiol-linkers, asdiscussed above. In some embodiments, the thickness of each of the twoportions 24A and 24B of the thermal intermediate structure ranges fromabout 2 to 50 microns. After the two portions 24A, 24B of the thermalintermediate structure 24 are formed on the two opposing surfaces of thedie 14 and the heat spreader 16, the die and heat spreader are broughttogether and the free ends of the two portions 24A and 24B arestructurally joined into thermal intermediate structure 24.

FIG. 6 is a flow chart illustrating several methods according to anembodiment. Thus, a method 611 may (optionally) begin at block 621 withcoating at least one surface of least one of a heat sink and of a diewith a metal and, at block 623, treating at least one end of at leastsome of a plurality of carbon nanotubes by applying organic moietiesthereto. In an embodiment, the metal is gold or a gold alloy.

At block 625, in an embodiment, the applying moieties process includestreating the at least one end of some of the plurality of nanotubes byforming an amide based linkage and a thiol based linkage thereon. In analternative step 627 (optional), the applying moieties includes treatingthe at least one end of some of the plurality of nanotubes by forming anamide based linkage thereon. In some embodiments, a further step 629 istethering one end of the at least some of the carbon nanotubes of theplurality of carbon nanotubes to the metal

In a method embodiment illustrated in FIG. 7, a process 700 comprises,in block 723 oxidizing the nanotubes ropes in acid to cut them intoshort nanotubes with open ends having carboxyl linkages attachedthereto. In block 725 the process includes applying organic linkingmoieties at the open ends. In an embodiment, the organic moietiescomprise an amide linker. In an embodiment the organic moieties alsocomprise a thiol linker. In an embodiment, the organic moieties comprisea thiol linker and an amide linker.

In an embodiment, a block 727 comprises tethering an end of the shortnanotubes to a surface of a first object. In an embodiment,a block 729comprises placing a surface of a second object in contact with anotherend of the short nanotubes to form a thermal path between surface of thefirst object and the surface of the second object.

FIG. 8 is a depiction of a computing system according to an embodiment.One or more of the embodiments of apparatus with one or more dies havinga thermal intermediate structure comprising a plurality of carbonnanotubes, some of which are tethered to at least one of the die and theheat sink with a thermal interface may be used in a computing systemsuch as a computing system 00 of FIG. 8. The computing system 700includes at least one processor (not pictured), which is enclosed in amicroelectronic device package 810, a data storage system 812, at leastone input device such as a keyboard 814, and at least one output devicesuch as a monitor 816, for example. The computing system 800 includes aprocessor that processes data signals, and may include, for example, amicroprocessor available from Intel Corporation. In addition to thekeyboard 814, an embodiment of the computing system includes a furtheruser input device such as a mouse 818, for example.

For the purposes of this disclosure, a computing system 800 embodyingcomponents in accordance with the claimed subject matter may include anysystem that utilizes a microelectronic device package, which mayinclude, for example, a data storage device such as dynamic randomaccess memory, polymer memory, flash memory and phase change memory. Themicroelectronic device package can also include a die that contains adigital signal processor (DSP), a micro-controller, an applicationspecific integrated circuit (ASIC), or a microprocessor.

Embodiments set forth in this disclosure can be applied to devices andapparatus other than a traditional computer. For example, a die can bepackaged with an embodiment of the thermal interface material and bufferlayer, and placed in a portable device such as a wireless communicatoror a hand held device such as a personal data assistant or the like.Another example is a die that can be coupled to a heat sink with anembodiment of the thermal interface material and buffer layer and placedin a dirigible craft such as an automobile, a watercraft, an aircraft ora spacecraft.

The apparatus 10, substrate 12, die 14, heat spreader 16, integratedcircuit 20, solder bumps 22 thermal intermediate structure 24 and theplurality of carbon nanotubes and organic moieties which form thermalintermediate structure 24 may all be characterized as “modules” herein.Such modules may include hardware circuitry, and/or a processor and/ormemory circuits, software program modules and objects, and/or firmware,and combinations thereof, as desired by the architect of the apparatus10 and system 800, and as appropriate for particular implementations ofvarious embodiments. For example, such modules may be included in asystem operations simulation package, such as a software electricalsignal simulation package, a power usage and distribution simulationpackage, a thermo-mechanical stress simulation package, a power/heatdissipation simulation package, and/or a combination of software andhardware used to simulate the operation of various potentialembodiments.

It should also be understood that the apparatus and systems of variousembodiments can be used in applications other than for coupling and heattransfer between dice and heat sinks and thus, these embodiments are notto be so limited. The illustrations of apparatus 10 and system 700 areintended to provide a general understanding of the elements andstructure of various embodiments, and they are not intended to serve asa complete description of all the features of compositions, apparatus,and systems that might make use of the elements and structures describedherein.

Applications that may include the novel apparatus and systems of variousembodiments include electronic circuitry used in high-speed computers,communication and signal processing circuitry, data transceivers,modems, processor modules, embedded processors, and application-specificmodules, including multilayer, multi-chip modules. Such apparatus andsystems may further be included as sub-components within a variety ofelectronic systems, such as televisions, cellular telephones, personalcomputers, workstations, radios, video players, vehicles, and others.

It should be noted that the methods described herein do not have to beexecuted in the order described, or in any particular order. Moreover,various activities described with respect to the methods identifiedherein can be executed in serial or parallel fashion.

Although specific embodiments have been illustrated and describedherein, it should be appreciated that any arrangement calculated toachieve the same purpose may be substituted for the specific embodimentsshown. This disclosure is intended to cover any and all adaptations orvariations of various embodiments. It is to be understood that the abovedescription has been made in an illustrative fashion, and not arestrictive one. Combinations of the above embodiments, and otherembodiments not specifically described herein will be apparent to thoseof skill in the art upon reviewing the above description. Thus, thescope of various embodiments includes any other applications in whichthe above compositions, structures, and methods are used.

It is emphasized that the Abstract of the Disclosure is provided tocomply with 37 C.F.R. §1.72(b), requiring an abstract that will allowthe reader to quickly ascertain the nature of the technical disclosure.It is submitted with the understanding that it will not be used tointerpret or limit the scope or meaning of the claims. In addition, inthe foregoing Detailed Description, it can be seen that various featuresare grouped together in a single embodiment for the purpose ofstreamlining the disclosure. This method of disclosure is not to beinterpreted as reflecting an intention that the claimed embodimentsrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter lies in lessthan all features of a single disclosed embodiment. Thus the followingclaims are hereby incorporated into the Detailed Description, with eachclaim standing on its own as a separate preferred embodiment. In theappended claims, the terms “including” and “in which” are used as theplain-English equivalents of the respective terms “comprising” and“wherein,” respectively. Moreover, the terms “first,” “second,” and“third” etc. are used merely as labels, and are not intended to imposenumerical requirements on their objects.

1. A process: coating at least one surface of least one of a heat sinkand of a die with a metal; oxidizing carbon nanotubes ropes in sulfuricand nitric acids, whereby the carbon nanotubes ropes are cut into aplurality of short carbon nanotubes with open ends having carboxyllinkages attached thereto; treating at least one end of at least some ofa plurality of carbon nanotubes by applying organic moieties thereto;and tethering one end of the at least some of the carbon nanotubes ofthe plurality of carbon nanotubes to the metal.
 2. The process of claim1 wherein the metal is selected from the group consisting of gold andgold alloys.
 3. The process of claim 2, wherein the treating the atleast one end of some of the plurality of nanotubes comprises forming anamide based linkage thereon.
 4. The process of claim 2, wherein thetreating the at least one end of some of the plurality of nanotubescomprises forming an amide based linkage and a thiol based linkagethereon.